This invention relates to a cooling air ducting system in the high-pressure turbine section of a gas turbine engine, in which a portion of the air flow which exits from the compressor section of the engine and bypasses the combustion chamber of the gas turbine is ducted via a first pre-swirl system provided in a diaphragm into a pre-swirl chamber arranged upstream of the first stage turbine rotor disk and is fed from this pre-swirl chamber, in particular, to the air-cooled blades of this rotor disk for cooling purposes, and in which another portion of this air flow is applied to the face of the first stage turbine rotor disk via a second air transfer system which, when viewed in the radial direction, is arranged further inward than the first pre-swirl system. For background art, reference is made to Specification EP 0 757 750 B1 and DE 29 13 548 C2, in particular.
Cooling air ducting systems in accordance with the generic part of claim 1 are known in a great variety of designs. In these designs, an arrangement termed pre-swirl system xe2x80x94for example in the form of a suitable vane cascade or in the form of holes in said diaphragm whose axes extend partly in the circumferential direction relative to the engine rotational axisxe2x80x94is used to impart a swirl on the air flow entering the pre-swirl chamber which is arranged downstream of said diaphragm and upstream of the first stage turbine rotor disk, said swirl being co-directional with the direction of rotation of the turbine rotor disk. This ensures that this cooling air flow or this air flow entering the pre-swirl chamber, respectively, takes a favorable route, relative to the surface of the rotating rotor disk, with the temperature of this cooling air flow being advantageously reduced and the cooling efficiency being further improved by the deflection of the air flow in the pre-swirl system.
Said pre-swirl system is, in most cases, arranged quite far on the outside in the radial direction (relative to the engine rotational axis), i.e. relatively close to the main gas path of the engine in which the hot working gas is carried. Thus, a sufficiently cold air flow is available for the cooling of the blades carried by this turbine rotor disk, this airflow not being excessively heated up previously on the rotor disk. In order to cool the area of the rotor disk which is located further inward in the radial direction, a portion of the air flow which is compressed in the compressor and which bypasses the combustion chamber of the gas turbine is applied to this further inward area, in which arrangement a second air transfer system is, or can be, provided for this portion of the air flow. In the state of the art according to Specification DE 29 13548 C2 mentioned secondly at the beginning, the air flow which is routed via the second air transfer system to the face of the first stage turbine rotor disk is essentially separate from the air flow ducted via the first pre-swirl system, i.e. in this known state of the art, the cooling air through the second air transfer system will not, or only minimally, enter said pre-swirl chamber.
The air supplied via the second air transfer system shows only a weak swirl, which already becomes apparent from the fact that it is relatively far on the inside with respect to the radial direction. This is one of the reasons for the relatively small cooling efficiency of this air flow which is directed to the rotor disk surface. In addition, the relatively small swirl factor (this is the quotient of the circumferential velocity of the air flow and the circumferential velocity of the rotor disk) which ensues from the weakness of the swirl results in a high relative total temperature of the rotor disk which, as is known to the expert, has a negative effect on the life of the rotor disk.
If the second, radially further inward air transfer system is provided in the form of a labyrinth-type seal, as frequently encountered in the state of the art, the air supplied via this system will be heated additionally by the frictional effects in the labyrinth seal. Altogether, the radially further inward area of the turbine disk will be cooled much less than its radially further outward area. As a result of this, an undesirably high temperature gradient can occur in the rotor disk in the radial direction.
A broad aspect of the present invention is to provide remedy to the above problematics.
It is a particular object of this invention to provide the second air transfer system as a pre-swirl system which also exits to the pre-swirl chamber. Preferably, a sealing system is provided between a section of the diaphragm confining the pre-swirl chamber and the turbine shaft section adjacent to this diaphragm section, this sealing system being less permissive of leaking air than the labyrinth-type seal arrangements commonly used in this application.
According to the present invention, the cooling air is ducted towards the rotor disk surface or towards the face of the first stage turbine rotor disk, respectively, both in the radially further outward and in a radially further inward area by way of separate pre-swirl systems. Accordingly, for the conveyance of cooling air, a second (secondary) pre-swirl system is provided besides the first pre-swirl system known in the state of the art. These two pre-swirl systems connect to the same pre-swirl chamber upstream of the rotor disk, this pre-swirl chamber being appropriately enlarged, i.e. extending radially further inward. This provides for an extremely effective and radially more uniform cooling of the rotor disk. This secondary pre-swirl system will also lead to a change of the swirl factor, as a result of which the relative total temperature of the rotor disk will be lowered and the radial temperature gradients in the rotor disk generally be reduced considerably.
The provision of a facultative, improved sealing system with less air leakage (e.g. a brush-type seal as disclosed in the initially cited Specification EP 0 757 750 B1) will enhance the efficiency of the second or secondary pre-swirl system, among others by the pump mass flow drawn by the rotating rotor disk. Advantageously, the mass of a brush-type sealing system is lower than that of a conventional labyrinth-type seal.
Further objects and advantages of this invention will become apparent from the following detailed description of a preferred embodiment which is shown in partial and principal representation only. A cooling air ducting system according to the present invention is shown schematically in the one accompanying FIGURE, in which all of the features described in detail can be essential for the invention.
Reference numeral 1 indicates the first stage rotor disk of the high-pressure turbine section of a gas turbine engine not further detailed herein, with the outer circumference of the rotor disk carrying, as usual, a number of rotor blades 2 (shown only partly herein) which extend into working gas-carrying main gas path 3 of the engine. As usual, stationary stator vanes 5 are arranged upstream of the rotor blades 2, these rotor blades 2 rotating with the rotor disk 1 about a rotational axis 4 represented in the lower part of FIGURE, i.e. the working gas flows the gas path essentially in the direction of the arrow A. While the direction of arrow A corresponds to the axial direction of the engine and is accordingly also designated with A in the following, the radial direction R is vertical to the direction A and extends from the rotational axis 4 of the engine, which is centrally inward and parallel to axial direction A, to the outside.
As usual, a combustion chamber (not shown) and a compressor section of the engine are arranged in this sequence upstream of the high-pressure turbine section which is only partly represented. Accordingly, when viewed against the axial direction A, the combustion chamber and the compressor section follow in this sequence to the left of the engine section shown in the FIGURE. As is known, the air flow discharged from the compressor does not entirely enter the engine combustion chamber, to be energetically enriched therein by the combustion of fuel, but partly passes by the combustion chamber, this bypassed portion not being further heated up and, therefore, being available as sealing air for the turbine interior and as cooling air for those components requiring cooling in the turbine section.
In particular the rotor blades 2 and the first stage rotor disk 1 carrying these rotor blades require intensive cooling by a relative cold air flow which, throughout the FIGURE, is indicated by the arrows 6, with the reference numeral 6 being accordingly used in the following to make reference to this air flow which, as already explained, bypasses the combustion chamber, and to portions of this airflow. As usual, this air flow 6 is applied to the face 1a of the rotor disk 1, i.e. at least a portion of this air flow 6 enters a pre-swirl chamber 7 arranged upstream of the rotor disk 1 which is separated from the engine interior 8 by a diaphragm 9, with this engine interior 8 again being arranged upstream when viewed in the axial direction A. From this pre-swirl chamber 7, the cooling air flow 6 is fed through cooling air ducts 14 in the rotor disk 1 to the interiors of the partly hollow, air-cooled rotor blades 2, as illustrated in highly simplified form. This cooling air, which is already heated, is then routed through film cooling holes (not shown) in the surfaces of the rotor blades 2 to the main gas path 3.